Modulation



N. E. LINDENBLAD MODULATION Origirial Filed April 5, 1932 Sept. 5, 1939.

A C SOURCE INVENTOR /V/L.$ E. l/ADfMQLAD BY #g MW ATTORNEY 4 'atented Sept. 5, 1939 UNITED STATES PATENT OFFICE MODULATION Nils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware tion April 2, 1936, Serial No. 72,245

13 Claims.

This invention, which is a division of my coanding applications Serial #603,310 filed in the nited States Patent Oifice, April 5, 1932, patent 2,052,576 dated September 1, 1936 and Serial 698,496 filed in the United States Patent Ofiice ovember 17, 1933, patent #2,061,947 dated No- :mber 24, 1936, relates to the radio art and apartains especially to the modulation and electro- .agnetic propagation of radio waves, particurly in the range of wave lengths below two .eters and of the order of frequencies above one indred fifty million (150,000,000) cycles per :cond.

One object of my present invention is to prode a modulation system for extremely short ave length oscillations of electrical energy.

My present invention will be described more 1lly hereinafter from which many other ob- :cts, features and advantages of my present inquency by-pass condenser 4 which fixes this point on 34 and the adjacent end of 24 at ground audio frequency potential. One purpose of 4 is to complete the audio frequency circuit through 24 and tubes 20. The impedances of tubes are shunted by a biasing resistance 33 which is in series with a grid leak resistance 30 connected between the grids and cathods of tubes 26 and 28. Direct current potential for both the modulator tubes 20, and the magnetic modulator tubes 26 and 28, is supplied through conductor 22. The modulator reactor or audio choke 24 is chosen so as to have practically no direct current resistance. Consequently, the grids and filaments of the modulator tubes 26, 28 will be at the same direct current current potential except for the drop in direct current potential across resistor 30. However, since the current drawn through choke 24 is constant because of its inzntion will become self apparent. herent action, the voltage across resistor 33 con- 20 In the accompanying drawing, the single figure nected between the anodes and cathodes of the lOWS means for multiplying high frequency modulator tubes 29, will vary according to the llations and modulating the same. modulating potentials due to the varying current In my United States application #603,310 menfl w in 33. Con q n ly, t voltage p h oned above, I have shown novel means for progrids of the modulator tubes 26, 28 will vary as icing oscillations multiplying the frequency of a result of Which a yi mounts o Current 1e produced oscillations, modulating the multi- Will be drawn absorbed from Circuit lied oscillations, and propagating the same. In The arrangement shown e O e s e ad- 1e present application I disclose an additional Vantage that blocking nde se Such as used leans for modulating oscillations produced in in the modulation circuit of the parent applieamy manner such as for example, oscillations as tiOn, are unnecessary. Moreover, s arrangeroduced in said application. In describing this meht Shown has the ed advantage that, eovel modulation system reference will be made Cause Of a ce couplin the circuit is eX- )the single figure of the drawings. The waves tremely Stable, of fine fidelity, and gre the modulated may be supplied from any source Simplifies Operation 5 a line AS of the character described in said The filament circuits 32 of t dul t tubes pplication, and when modulated in a manner may be tuned as in the parent pp a ion but ascribed more in detail hereinafter may be supneed not necessarily be tuned in the present lied from the line As to any load hi h may b rangement. When the filament circuits of the line or an antenna system. A magnetic m d absorber tubes are tuned the filaments and cirttOI' MM comprising tubes 26 and 28 i used cuits are balanced or at ground radio frequency )absorb' energy from line AS. The tubes have potential- The Circuit 2 y be tuned to t e ieir grid electrodes connected as shown by byfrequency of the Waves assing condensers 6 and 8 to maximum voltage The anodes 0f tubes 25 and 25 y b left oints l and 9 on the line AS or, in other words, fl that is, Completely nnected, 01 5 t high impedance points. The absorption ciry be Short eil'euited, 0 y be o ec ed as 1117 is completed by connecting the filaments of Shown y a Circuit tuned to the frequency of 1e tubes 26 and 28 together by the circuits 32. t ves in he modulation circuit is completed by co n et- The solenoids l4 of the magnetic modulator are 1% a point on the impedance 34, which may energized by a variable source I 6 in a circuit in- 5Q lpply the heating current to the filaments of eluding said solenoids and a variable resistance ibes 26 and 28, to a reactor 24 which is conl8. The solenoids produce a magnetic fi d P ected as shown to the anodes of tubes 20 the allel to their axes which are at right angles with athodes of which are grounded. This point on respect to the electron paths of the tubes.

4 is also connected to ground by an audio fre- It has been found that if one attempts to modulate, with conventional schemes, the energy in the absorption circuit, for example, by-passing that circuit to ground through a variable impedance in the form of. electron discharge devices, variations in the direct current throughthe impedance device in accordance with. modulating potentials will produce only infinitesimal effects upon the energy in the absorption circuit. This is due to the fact that the capacitance of the device prevents any appreciable electron moving voltage to build up at these very high frequencies. Only by careful lining up of the electrons will it be possible to make them respond to these small voltage variations. Moreover, the low electron velocity within the ordinary tubes also mitigates against their use as modulators. However, with my improved tube absorbing circuit comprising tubes 26 and 28, modulation is readily accomplished as the characteristics of the tubes are greatly changed, with the application of the magnetic field thereto. This field is as shown perpen-r dicular to the normal path of the electron stream from the cathode to the anode.

This field causes the electrons emanating from the filaments to follow curved paths; so that the emitted electrons after leaving the filament are forced back and. are retained in large numbersin suspension about the cathode and in the grid space. Thus, by causing the electrons to be sus-' pended in orbits near the grid, due to the effect of the magnetic field, a greater number of electrons are available to be effected by modulating potentials'. The grids are in this case biased so that electrons of tangential motion versus the grid are at all times available in great numbers inthe extreme vicinity of the grid so that even though low, potentials of low or high frequency can spend work on the same with the result that absorption takes place. To vary the potential level upon the control grids of the magnetic modulator, thereby varying the absorption of energy by making a greater or smaller number of electrons available and thereby accomplishing modulation of the waves in the absorption circuit, modulation from 20 is applied to'33 to produce therein a potential drop characteristic of the signal variations which is impressed on the grids of the magnetic modulator.

I claim:

- 1. A system for absorbing high frequency energy from a high frequency circuit comprising an electron discharge device having an electron emitting cathode, and'a control electrode, means for connecting said control electrode to said high frequency circuit, a connection between the cathode of said device and a different point on said high frequency circuit, an audio frequency impedance of loW direct current resistanc connected at one terminal to the cathode of said device, an additional impedance connecting the other terminal of said audio frequency impedance to the control electrode of said device, and means for applying potentials to said last named impedance which vary at signal frequency said control electrode potential varies at signal frequency and said control electrode-cathode circuit absorbs energy from said high frequency circuit in accordance with variations in the potentials of said control electrode.

2. A modulating system comprisinga high frequency circuit having voltage maximum points, said circuit having flowing therein high frequency currents to be modulated, a pair of electron discharge devices each having an electron emitting cathode and a cold electrode, means connecting said cold eelctrodes to voltage maximum points i said high frequency circuit, impedance mear connected to the cathodes of said devices, an ad ditional impedance connecting said first imped ance to the cold electrodes of said devices an means for applying a potential which varies 2 signal frequency in shunt to said first named im pedance for varying the conductivity of said de vices thereby varying the amount of energy d1 verted from said high frequency circuit. '3. Apparatus as recited in claim 1 wherei means is provided for subjecting the electro stream of said device to a magnetic field.

4. Apparatus as recited in claim 2 includin means for applying a magnetic field to said elec tron discharge devices to thereby improve th operation thereof.

5. In a system for absorbing high frequency en ergy from a high frequency circuit in accordanc with signals, an electron discharge device havin an electron emitting cathode, and a control elec trode, means for connecting said control elec trode and cathode to spaced points on said higi frequency circuit, a reactance of low direct cur rent impedance connected to said electron emit ting cathode, an impedance connected to sai reactance, an impedance connecting said react ance to the control electrode in said device an means for producing currentflow insaid'firs named impedance which varies in accordanc with signal potentials.

6. In a system for absorbing high frequenc; energy from a high frequency circuit in Whicl said energy is flowing at signal frequency, a pai of electron discharge devices, each having a1 electron emitting cathode and'a control elec trode, a tuned circuit connecting the control elec trodes of said discharge devices to points of higl impedance on said high frequency circuit, a con nection between the cathodes of said devices, a1 impedance and a reactor 'of loW direct curren impedance connecting the control electrodes 0 said electron discharg devices to the cathodes 0 said electron discharge devices and means fo: applying potentials which vary at signal fre quency to said impedance.

7. In a system for absorbing high frequenc: energy from a high frequency circuit in whicl said energy flows at signal frequency, a pair 01 electron discharge devices, each having an elec tron emitting cathode and a control'electrode areactive circuit connecting said control electrodes to points of high impedance on said higl frequency circuit, means connecting said cathodes together, an additional'thermionic discharg( device having its anode connected to the cathode: ofs'aid first pair of discharge devices, a reactor 0; low direct current impedance in said connection an impedance connected between the contro electrodes and cathodes of said first named devices, an impedance connected between the anode and cathode of saidadditional device and mean: for'varying the anode to cathode impedance 01 said additional device at signal frequency.

8. A system as recited in claim 6 wherein saic' discharge devices each include an additional electrode and in which said additional electrodes are connected together.

9. A system as recited in claim 7 wherein said first named discharge devices each have an additional electrode and wherein said additional electrodes are connected by a reactive circuit.-

10. In a system for absorbing'radio frequency energy from a radio'frequency circuit in accordance with signals to thereby modulate said radic frequency energy at signal frequency, an electron discharge device having an electron emitting cathode, and an additional electrode, means for connecting said additional electrode to said radio frequency circuit, separate means for connecting said cathode to a second point on said radio frequency circuit, a reactance of low direct current impedance connected to said electron emitting cathode, a connection of low impedance to audio frequency energy connecting said reactance to a point of substantially fixed potential, an impedance connecting said reactance to said additional electrode in said device and means for producing potentials on a terminal of said impedance which vary in accordance with signal potentials.

11. A system as recited in claim 10 wherein magnetic means is provided for producing a magnetic field perpendicular to the normal path of the electron stream from the cathode to said additional electrode to thereby improve the operation of the modulator.

12. In a modulation system, a high frequency circuit having flowing therein high frequency currents to be modulated, a pair of electron discharge devices each having an electron emitting cathode and an additional electrode, means connecting said additional electrodes to spaced points on said high frequency circuit, impedance means connected to the cathodes of said devices, an additional impedance connecting said first impedance means to the additional electrodes of said devices, and means for applying a potential which varies at signal frequency to said first named impedance means for varying the conductivity of said devices, thereby varying the amount of energy diverted from said high frequency circuit.

13. In a system for absorbing high frequency energy from a circuit in which high frequency energy flows to thereby modulate said energy in accordance with signals, an electron discharge device having an electron emitting cathode and a control electrode, a tuned circuit connecting said control electrode to a point of high impedance on said high frequency circuit, separate means connecting said cathode to a second point on said high frequency circuit, a reactor of low direct current impedance and an impedance in series connecting the electron emitting cathode of said device to a point of substantially fixed potential, a condenser in shunt to said reactor and impedance, an additional impedance connecting a point intermediate said reactor and said first named impedance to the control electrode of said discharge device and means for varying the current flow in said first named impedance at signal frequency.

NILS E. LINDENBLAD. 

